Logging While Pulling

ABSTRACT

The disclosure includes a system, method, and tool for logging while pulling. The disclosed system includes a tool and a bottom hole assembly, and the tool engages with the bottom hole assembly. The tool includes an elongated body, a retarder positioned on the elongated body, and a locking ring positioned on the elongated body. The retarder has at least one point of contact with an interior surface of a drill pipe. The disclosed method includes assembling the tool, providing a landing ring on a bottom hole assembly, free dropping the tool to the bottom hole assembly, and engaging the landing ring of the bottom hole assembly with the locking ring of the tool so that a portion of the tool extends below the bottom hole assembly.

BACKGROUND

Embodiments of the inventive subject matter generally relate to logging of a wellbore after drilling thereof. Particularly, embodiments of the inventive subject matter relate to logging of a wellbore as a drill string is pulled upwardly therethrough.

Various techniques are used to log information from a wellbore about subsurface formations, including wireline logging, measurement while drilling (MWD), and logging while drilling (LWD). Wireline logging techniques can involve lowering a measurement tool into a wellbore on the end of a wireline (e.g. a cable), measuring wellbore and subsurface formation parameters as a function of depth while the measurement tool is pulled up the wellbore, and transmitting various parameters through the wireline to the surface. MWD techniques can involve collecting data of downhole conditions and movement of a drilling assembly during the drilling operation. LWD techniques can involve focusing more on measurement of formation parameters than on movement of the drilling assembly. Wireline logging can have a high cost and time footprint because the drill string must be removed from the wellbore before the measurement tool can be lowered into the wellbore. Likewise, MWD and LWD can have a high cost because the measurement tools must endure drilling environments within the wellbore. Thus, alternative techniques are desired.

SUMMARY OF THE INVENTION

Embodiments of the disclosed inventive subject matter may include a system, method, and tool for logging while pulling.

In embodiments, the disclosed system comprises a tool and a bottom hole assembly, wherein the tool is engaged with the bottom hole assembly. The tool may have an elongated body, a retarder positioned on the elongated body, and a locking ring positioned on the elongated body. The retarder may comprise at least one point of contact with an interior surface of a drill pipe.

In embodiments, the disclosed method comprises assembling a tool having a locking ring and a retarder positioned on an elongated body of the tool, providing a landing ring on a bottom hole assembly, free dropping the tool to the bottom hole assembly, and engaging the landing ring of the bottom hole assembly with the locking ring of the tool so that a portion of the tool extends below the bottom hole assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed embodiments may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 shows an elevational view of an embodiment of a tool for logging while pulling according to the disclosed inventive subject matter.

FIG. 2 shows a bottom view of an embodiment of the tool according to the disclosed inventive subject matter.

FIG. 3 shows an elevational view of an embodiment of a drill string and bottom hole assembly for logging while pulling according to the disclosed inventive subject matter.

FIG. 4 shows a cross-sectional view of an embodiment of a bottom hole assembly of a drill string, taken along sight line 4-4 shown in FIG. 3.

FIG. 5 shows a cross-sectional view of an embodiment of a system according to the disclosed inventive subject matter, the system being in a borehole.

FIG. 6 shows a flow diagram of an embodiment of a method for logging while pulling according to the disclosed inventive subject matter.

FIG. 7 shows a sample log generated by an embodiment of the disclosed inventive subject matter.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

The description that follows includes examples of systems, methods, techniques, and tools that embody the disclosed inventive subject matter. However, it should be understood that the described embodiments may be practiced without describing certain specific details that are well known—such as well-known structures, materials, techniques, and configurations—in order not to obfuscate the description of the inventive subject matter. For instance, although the description of embodiments refers to sensors in the logging subs of the tool of the inventive subject matter, the electrical connections of the sensors with various other components may not be described in detail because such connections and components are within the skill of the art.

As will be appreciated by one skilled in the art, aspects of the disclosed inventive subject matter may be embodied as a system, method, or tool. Accordingly, aspects of the disclosed inventive subject matter may take the form of an entirely structural embodiment, a functional embodiment, a methodological embodiment, or an embodiment combining these various aspects of the inventive subject matter.

FIG. 1 shows an elevational view of an embodiment of a tool 100 for logging-while-pulling according to the disclosed inventive subject matter. The tool 100 may have an elongated body 120 having an upper section 121 and a lower section 122. The upper section 121 of the elongated body 120 may have logging subs 180 positioned therein, shown in FIG. 1 with dashed lines. The logging subs 180 may have an induction sensor, a natural gamma sensor, a gamma spectroscopy sensor, a neutron sensor, a density sensor, or combinations thereof, for example. In embodiments, the logging subs 180 may have more than one of the same type of sensors. In embodiments, the logging subs 180 may have a combination of different types of sensors. The lower section 122 of the elongated body 120 may have logging subs 185 positioned therein, shown in FIG. 1 with dashed lines. In one or more embodiments, the logging subs 185 may have monopole and dipole sonic sensors or resistivity sensors, or combinations thereof, for example. In one or more embodiments, the logging subs 185 may have more than one of the same type of sensors, or a combination of different types of sensors. In one or more embodiments, the logging subs 180 of the upper section 121 of the elongated body 120 may have sensors that are operational in lined and unlined boreholes while the logging subs 185 of the lower section 122 of the elongated body 120 may have sensors that are operational only in unlined boreholes (i.e. boreholes that have no lining, or casing). Each of the sensors of logging subs 180 and 185 may measure individual geophysical parameters. Because of the flexibility for including different types of logging subs 180 and 185, the logging subs 180 and 185 of the tool 100 may be stackable so as to have any number of separate logging subs 180 and 185 attached in a single tool 100.

The elongated body 120 of the tool 100 may have batteries 125, a time-based memory 126, and a motion sensor 127 positioned therein. The batteries 125, time-based memory 126, and motion sensor 127 are shown in FIG. 1 with dashed lines. The batteries 125 may provide power for operation of the tool 100. Data from logging may be stored in the time-based memory 126. The motion sensor 127 may detect motion of the tool 100 in a borehole. The motion of the tool 100 in the borehole may be stationary or moving (e.g., during withdrawal), and data from logging may be differentiated between stationary periods and moving periods due to motion detection of the motion sensor 127.

The tool 100 may have a locking ring 130 positioned on the elongated body 120 of the tool 100 between the logging subs 180 of the upper section 121 of the elongated body 120 and logging subs 185 of the lower section 122 of the elongated body 120. In one or more embodiments, the logging subs 180 of the upper section 121 of the elongated body 120 that are operational in lined boreholes are positioned above the locking ring 130, and the logging subs 185 of the lower section 122 of the elongated body 120 that are operational in unlined boreholes are positioned below the locking ring 130. The locking ring 130 may be machined to lock into the landing ring of the locking sub as discussed in FIGS. 4 and 5 below.

In an embodiment, the tool 100 may have a retarder 140 positioned on the elongate body 120 adjacent end 123 of the tool 100. In other embodiments, the elongated body 120 of the tool 100 may be positioned in a center 141 of the retarder 140, alternatively, the elongated body 120 of the tool 100 may be positioned through a center 141 of the retarder 140. The retarder 140 may have a general contour resembling that of an umbrella. The contour and shape of the retarder 140 may serve to control the speed of the decent of the tool 100 into the borehole and to center the tool 100 within the interior of the drill pipe and any drill collars for correct positioning after free-drop (the method and detail of the free drop are described below). The retarder 140 may generally be a rigid structure, and may be formed of materials suitable for use in bottom hole assemblies such as metals, polymers, or combinations thereof. In embodiments, the retarder 140 may be attached to the end 123 of the tool 100. In other embodiments, the retarder 140 may be integrally formed with the end 123 of the tool 100. In an embodiment, the locking ring 130 is positioned on the elongated body 120 below the retarder 140.

In one or more embodiments, the length B of the tool 100 may be about 7 meters. As can be seen, the tool 100 is simple in construction. The simplicity reduces capital cost, and additionally, the simple configuration allows the tool 100 to free drop easily within a drill string without catching on bends, connections, and other inconsistencies in drill pipes. In embodiments, free drop occurs without a tether attached to the tool. In embodiments, during free drop the tool may reach free fall velocity as the tool falls through the drill string to the bottom hole assembly. In embodiments, during free drop the tool may reach velocities less than free fall due to frictional forces of the tool against, for example, the inner wall(s) of a drill string. In embodiments, the velocity of the tool through the drill string may vary as the tool travels through the drill string to the bottom hole assembly. For example, the speed of the tool may decrease as the tool travels through curves of the drill string, the speed of the tool may increase as the tool travels through straight portions of the drill string, the speed of the tool may increase or decrease as the tool travels through different zones in the drill string, or combinations thereof. In an embodiment, the retarder 140 may be the only source of frictional force against the drill string. In an embodiment, the retarder 140 may be a source of frictional force against the drill string continuously, intermittently, or combinations thereof

FIG. 2 shows a bottom view of an embodiment of the tool 200 according to the disclosed inventive subject matter. Generally, the profiles of the elongated body 220, locking ring 230, and retarder 240 may take shapes that easily fall through a vertical longitudinal hollow interior of a drill pipe and drill collar, and the profiles of the elongated body 220, locking ring 230, and retarder 240 may be the same as one another or different from one another. In FIG. 2, the elongated body 220, locking ring 230, and retarder 240 of the tool 200 are shown to have concentric-circular profiles. In an alternative embodiment, the profile of the elongate body 220 may be circular while the profile of the locking ring 230 may be square and the profile of the retarder 240 may resemble a star-shape, for example. In an alternative embodiment, the profile of the elongate body 220 may be octagonal while the profile of the locking ring 230 may be square and the profile of the profile of the retarder 240 may be square, for example. In other embodiments, the above-described embodiments for the profiles of the elongated body 220, locking ring 230, and retarder 240 may be combined.

Because the retarder 240 may function to control the speed of the tool 200 as the tool 200 free drops within the vertical longitudinal hollow interior of a drill string and bottom hole assembly, in one or more embodiments the profile of the retarder 240 may have a triangular shape for three points of contact with the interior surface of the drill pipe and drill collars, alternatively, the profile of the retarder 240 may have a rectangular shape for four points of contact with the interior surface of the drill pipe and drill collars, alternatively, the profile of the retarder 240 may have a pentagonal shape for five points of contact with the interior surface of the drill pipe and drill collars, and so on until myriad number of points of contact may be made using a circular profile for the retarder 240, for example. In other embodiments, the profile of the retarder 240 may resemble a star having any number of points of contact with the interior surface of the drill pipe and/or drill collars. In other embodiments, the profile of the retarder 240 may resemble any number of fan or propeller blades extending radially outwardly from the elongate body 220 of the tool 200 having any number of points of contact with the interior surface of the drill pipe and/or drill collars. In an embodiment, the point of contact may contact the interior surface of a drill string intermittently, continuously, or combinations thereof.

As shown in FIG. 2, the locking ring 230 may extend radially outwardly from the elongated body 220, and the retarder 240 may extend radially outwardly from the elongated body 220 further than the locking ring 230. In one or more embodiments, the retarder 240 may have a width approximately equal to a width of the locking ring 230.

In one or more embodiments, the logging subs may be slimline tools and may have a width (or diameter if circular in profile) of about 50 millimeters or less. In FIG. 2, the diameter B of the logging subs 285 (shown with dashed lines) may be about 50 millimeters or less. The total width (or diameter if circular in profile) of the tool of the inventive subject matter may be about 75 millimeters or less. In FIG. 2, the diameter C of the tool 200 may be about 75 millimeters or less.

In one or more embodiments, the locking ring 230 may be attached to an outer surface 229 of the elongate body 220, or the locking ring 230 may be integrally formed with the elongate body 220, for example.

FIG. 3 shows an elevational view of an embodiment of a drill string 300 and bottom hole assembly 394 for logging while pulling according to the disclosed inventive subject matter. The drill string 300 may have one or more drill pipe 391 connected in end-to-end in series and extending from the surface into a borehole drilled in a subsurface formation. The inner diameter of the drill pipe 391 of the drill string 300 may generally by greater than 75 millimeters. The bottom hole assembly 394 may be attached to the bottom of the drill string 300. The bottom hole assembly 394 may have one or more drill collars 350, a locking sub 355 connected to an end of the drill collar 350 opposite the drill string 300, a save sub 360 connected to an end of the locking sub 355 opposite the drill collar 350, and a drill bit 370 connected to an end of the saver sub 360 opposite the locking sub 355. The drill collar(s) 350, locking sub 355, and saver sub 360 of the bottom hole assembly 394 may generally have an outer diameter greater than an outer diameter of the drill pipe 391 of the drill string 300. Importantly, the drill bit 370 of the inventive subject matter may have a central opening 371 formed therein (shown with dashed lines). The central opening 371 may be concentric with the vertical longitudinal hollow interior of the drill pipe 391 of the drill string 300 and the drill collar(s) 350, locking sub 355, and saver sub 360 of the bottom hole assembly 394. The central opening 371 may generally have a diameter greater than about 75 millimeters. The central opening 371 may serve an additional function of sampling the wellbore using, for example, sample tubes through the central opening 371.

FIG. 4 shows a cross-sectional view of an embodiment of a bottom hole assembly 400 of the inventive subject matter, taken along sight line 4-4 shown in FIG. 3. The lower collar 451 of the drill collar 450 is connected to the locking sub 455. An end of the locking sub 455 opposite the lower collar 451 of the drill collar 450 is connected to the save sub 460. An end of the saver sub 460 opposite the locking sub 455 is connected to an end 472 of the drill bit 470. The central opening 471 of the drill bit may form a vertical longitudinal hollow interior extending from end 472 of drill bit 470 to opposite end 473 of drill bit 470. The drill collar(s) 450 may have walls 452 that are thicker than the walls of the drill pipe of the drill string. In one or more embodiments, the lower collar 451 of the drill collar(s) 450 may be made of a conductive or non-conductive material. In one or more embodiments, the lower collar 451 of the drill collar(s) 450 may be made of a ferrous (e.g., magnetic) or non-ferrous (e.g., non-magnetic) material.

The locking sub 455 of the bottom hole assembly 400 may have a landing ring 456 formed on an inside surface 459 of the walls 454 thereof. The landing ring 456 may be integrally formed or attached to the inside surface 459 of the walls 454 of the locking sub 455. In the embodiment shown in FIG. 4, the landing ring 456 may have a catch member 458 and groove 457 formed to catch and engage the locking ring of the tool. In one or more embodiments, the configuration of the landing ring 456 may take on a wedge shape that matches a corresponding wedge shape of the locking ring of the tool of the inventive subject matter. In one or more embodiments, the configuration of the landing ring 456 may have angled notches. The landing ring 456 may generally extend radially inwardly from the inside surface 459 of the walls 454 of the locking sub 455. The landing ring 456 and locking ring 455, which together may be referred to as the locking assembly, may engage and lock with one another using gravity and/or a static head of fluids in the drill string and/or wellbore.

In FIG. 4, the inner diameter F of the vertical longitudinal hollow interior of the drill collar(s) 450 and the saver sub 460 may be seen, the inner diameter D of the landing ring 456 of the locking sub 455 may be seen, and the diameter E of the central opening 471 of the drill bit 470 may be seen. Generally, diameters D, E, and F may be greater than about 75 millimeters. Any of diameters D, E, and F may be equal to or different from one another.

FIG. 5 shows a cross-sectional view of an embodiment of a system 500 according to the disclosed inventive subject matter. The system 500 may extend into a borehole 597, or wellbore. In

FIG. 5, the borehole 597 has been formed in a subsurface formation 595, and the walls 596 of the borehole 597 are unlined. The system 500 may have a tool 510 and a bottom hole assembly 594. In FIG. 5, the tool 510 is engaged with the bottom hole assembly 594.

The elongate body 520 of the tool 510 may contain logging subs 580 in upper section 521 and logging subs 585 in lower section 522. A battery 526, a time-based memory 527, and a motion sensor 528 may be positioned in the elongated body 520 of the tool 510 between the logging subs 580 and the logging subs 585. The outer diameter of the walls 529 of the elongated body 520 of the tool 510 may be about 75 millimeters or less. The retarder 540 of the tool 510 may be adjacent the inside surface 553 of the walls 552 of the lower collar 551 of the drill collar(s) 550.

The locking ring 530 of the tool 510 may engage the landing ring 556 of the locking sub 555 of the bottom hole assembly 594. The locking ring 530 may have a portion extending into the groove 557 of the landing ring 556 in order to engage the landing ring 556 and locking ring 530 and lock the landing ring 556 and locking ring 530 into position. The landing ring 556 may be attached to the wall 554 of the locking sub 555. In one or more embodiments, the locking ring 530 and landing ring 556 may have other configurations to engage and lock the tool 510 and bottom hole assembly 594, such as wedges, for example.

In one or more embodiments, the type of sensors within the stacked logging subs 580 and 585 of the tool 510 may be determined by geological requirements of the desired geophysical log for the subsurface formation 595. For example, if the lower collar 551 is non-conductive, sensors for electrical resistivity using an induction array could be positioned in the upper section 521 of the elongated body 520 of the tool 510. In one or more embodiments involving mining scenarios, a magnetic-susceptibility sensor may be the basal sensor of the logging subs 580 of the upper section 521 with a natural gamma or a gamma spectroscopy sensor attached above the magnetic susceptibility sensor, and sensors of logging subs 585 in the lower section 522 below the drill bit 570 may be connected to the induction sensor(s) in the upper section 521. In one or more embodiments, the landing ring 556 of the locking sub 555 may be placed between the gamma sensor and the induction sensor of the logging subs 580 of the upper section 521 of the elongated body 520 of the tool 510. The most beneficial position for the placement of the locking and landing ring is a position such that all the sensors requiring measurement in the open (un-lined) hole are clear of the bit. In borehole conditions where the stability of the hole cannot be assured then the locking ring may have to be placed differently on the assembly restricting the length of the tool assembly protruding below the bit. In one or more embodiments, a sonic dipole sensor may replace or be added to the magnetic-susceptibility sensor of the logging subs 580 of the upper section 521 of the elongated body 520 of the tool 510. Magnetic susceptibility may be advantageous during exploration whereas the sonic sensor may be more beneficial during a geotechnical investigation.

In one or more embodiments, at least a portion of the lower section 522 of the elongated body 520 of the tool 510 protrudes through the central opening 571 of the drill bit 570 and into the borehole 597 below the drill bit 570. The total length of the tool 510 and the length of the portion of the lower section 522 of the elongated body 520 of the tool 510 protruding through the central opening 571 below the drill bit 570 may be determined by accounting for the significance of the highest sensor measurement in the lowest section of the borehole 597 and by accounting for the expectation of stability in the lowest section of the unlined borehole 597. In one or more embodiments, a tool 510 having a total length of about 7 meters may have about 3 meters of the tool 510 extending below the drill bit 570 into the borehole 597 and about 3 meters of the tool 510 extending within the drill collar 550, for example.

FIG. 6 shows a flow diagram of an embodiment of a method 600 for logging while pulling according to the disclosed inventive subject matter. It should be understood the operations of the method as presented are by example and some operations may be substituted, added, rearranged or removed while still encompassing the inventive subject matter. Moreover, it should be understood the order of operations is not to be limited unless explicitly specified herein. The method 600 begins at block 602. At block 602, a landing ring is provided in a bottom hole assembly. The landing ring may be of a configuration of the embodiments shown in FIGS. 4 and 5 and described above. Flow continues to block 604.

At block 604, the tool having a locking ring may be assembled. Assembly may take place at a time near to completion of a bit run or the well bore, for example. The tool may be assembled according to embodiments of the inventive subject matter shown in FIGS. 1, 2, and 5 and described above. Flow then continues to block 606.

At block 606, the landing ring of the bottom hole assembly is engaged with the locking ring of the tool. Before engaging, the tool must be inserted into the drill string. Before insertion of the tool into the drill string, drilling operations are ceased or completed. After drilling operations have ceased and before insertion of the tool, the drill bit (and the drill string) may be pulled upward a sufficient distance above the base of the borehole to allow a portion of the logging tool to extend below the drill bit. In one or more embodiments, the drill bit of the bottom hole assembly may be lifted a distance approximately equal to a length of a drill pipe above a base of a borehole. In one or more embodiments, the drill bit of the bottom hole assembly may be lifted above the base of the borehole a distance approximately equal to a length of the portion of the tool below the locking ring of the tool minus the approximate distance of the opposite end of the drill bit to the landing ring of the locking sub. In one or more embodiments, a section of drill pipe may be separated from the drill string to expose the vertical longitudinal hollow interior of the remaining pipes in the drill string. Once the tool is inserted into the vertical longitudinal hollow interior of the drill string, the tool free drops, e.g. free falls, to the bottom hole assembly. In one or more embodiments, the tool may free drop, e.g. free fall, to the bottom hole assembly located in the base of the borehole. The free drop of the tool is a relatively small amount of time for insertion and engagement of the tool with the bottom hole assembly, thus reducing operational time and cost. The locking ring is placed on the tool in a location so that at least a portion of the lower portion of the tool passes through a central opening of the drill bit. The locking ring then engages with a landing ring by catching on a landing ring located in the locking sub positioned in the bottom hole assembly above the drill bit. The tool, or stack of logging subs, then locks in place so that a portion of the tool extends below the bottom hole assembly. In an embodiment, the portion of the tool may extend below a drill bit of the bottom hole assembly in an unlined borehole. Additionally, the tool may have a section extending above the drill bit in the lower collar of the drill collar of the bottom-hole assembly. In an embodiment, the portion of the tool extending below the bottom hole assembly may comprise a sonic dipole tool. The portion of the tool below and outside the drill bit may include sensors that operate only in unlined boreholes, and the portion of the tool above the drill bit may have sensors that operate in lined and unlined boreholes. The locking ring is positioned to allow the correct length of the portion of the lower section of the elongated body of the tool to pass through the drill bit. Drilling fluid may be circulated in the borehole to push the locking ring of the tool into tight engagement with the landing ring of the locking sub of the bottom hole assembly. Tight engagement allows the tool to be lifted as the drill bit is lifted from the borehole. Flow then proceeds to block 608.

At block 608, data is logged while pulling the tool and system upward through the borehole. During pulling, motion of the tool experiences movement periods and stationary periods. Stationary periods occur because drill pipe of the drill string must be disconnect or detached piece by piece from the drill string upon withdrawal from the borehole. During the moving and stationary periods, logging data may be recorded into the time-based memory of the tool. Time-based bit depth may be integrated with data in the time-based tool memory in order to provide a depth log. Motion of the tool and system are sensed by a motion sensor. Motion sensor data is used to generate logs of stationary data and moving data. The data are then differentiated according to stationary logging periods and moving logging periods during the steps of detaching and pulling, respectively. A depth log may be prepared by cross-referencing the pipe tally. A sonic dipole tool may be extended below the drill bit into the unlined borehole. In soft ground it is difficult to measure the shear wave values indicated by the guided waves in the borehole. The inventive subject matter may stack sonic signals in some or all of the pulses during the stationary period. In an embodiment, the tool may be suspended for a period in the borehole and sonic signals may be stacked so that from about 10 to about 20 pulses from the tool are added together and can be more easily interpreted in a manner of a Sonic Suspension Log. The sonic dipole tool may record in memory the stationary period while each drill pipe is detached from the drill string. A Continuous Sonic Log may be prepared in addition to the Sonic Suspension Log. Flow then proceeds to block 610.

At block 610, data is recovered from the tool and system of the inventive subject matter. The tool is recovered from the borehole by withdrawing the bottom hole assembly and disengaging the landing ring and locking ring. Data from the time-based memory may be downloaded at the surface. Alternatively, for a seabed drilling system, data may be recovered from the time-based memory remotely. A depth of the tool versus time may be determined if the inventive subject matter is used in combination with a depth measurement system. The moving periods M and stationary periods P may be combined with the data logs, such as those in log 700 of FIG. 7, to provide a depth log. The depth of the drill bit of the inventive subject matter may otherwise be determined by keeping a pipe tally. Alternatively, pulling of the drill string and bottom hole assembly may be assumed to be at a constant speed, and the drilling personnel may be instructed to note any stops in pulling other than stops related to disconnection of the drill pipe from the drill string. Flow then ends.

FIG. 7 shows a sample log 700 generated by an embodiment of the disclosed inventive subject matter. The log 700 contains data of a gamma log, a motion log, and a full sonic log. The data is taken over time, where time started at Time X and ended at Time Y, where Time Y is greater than Time X.

The tool and system may record the logs in the time-based memory. The logging subs may provide sensors for detecting data to be recorded, for example, gamma data and sonic data for the gamma log and full sonic log shown in FIG. 7. A motion sensor detects movement of the tool and system. Motion data 708 in the motion log clearly shows data for when movement has occurred. Stationary data 706 in the motion log clearly shows data for when the tool and system are stationary. The motion data provided by the motion sensor thus allows the log 700 to be divided into moving periods M and stationary periods S. During the stationary periods S, drill pipe may be detached from the drill string and bottom hole assembly. During the moving periods M, the tool and system may be further withdrawn from the borehole upward to the surface.

The gamma log shows data 702 in the moving period M and data 704 in the stationary period S. Likewise, the full sonic log shows data 710 in the moving period M and data 712 in the stationary period S. The data in the log 700 may clearly delineate the moving periods M from the stationary periods S. While the data in the gamma log and full sonic log may definitively indicate a stationary period S, ambiguity may be avoided because the motion sensor may clearly define movement of the drill bit, and this movement may be cross-checked with the log data of the gamma log, the full sonic log, and any other logs included in a log, such as the log 700 shown in FIG. 7.

In analyzing the data of logs, such as log 700, stationary data from logs other than the sonic log may be discarded. For example in FIG. 7, data 702 of the gamma log may be used and data 704 of the gamma log may be discarded. Data 712 from stationary period S of the sonic log may be stacked in signals of about 10 to 20 pulses. Stacking sonic signals during stationary periods S may identify slower return waves such as Stoneley waves that are more difficult to determine from logs in the moving period M. Data gathered by the full sonic log during the stationary periods S when multiple pulses are used may be equivalent to a Sonic Suspension Log. The full sonic log thus may contain a Sonic Suspension Log and a Continuous Sonic Log.

In scenarios where the inventive subject matter is used in combination with a depth measurement system, the moving periods M and stationary periods P may be combined with the data logs, such as those in log 700, to provide a depth log.

It is contemplated that embodiments of the inventive subject matter may be used in wireline coring applications.

The inventive subject matter allows geophysical logging of a drilled borehole without adding significant time to complete the borehole or significant capital cost in the tool. Very little time is added to log data using the inventive subject matter as compared to other geophysical logging devices because lowering the tool into the borehole using free drop of the tool is significantly faster than lowering the tool using a tether, wireline or pumping of drilling fluid. The time footprint for the inventive subject matter is thus closer to devices of LWD without the size, complexity and cost of LWD equipment.

There are particular situations where the inventive subject matter is advantageous. First, the inventive subject matter has particular advantages when used with recently innovated seabed drilling systems because such systems may require a remote drilling rig set on the seabed and operated either through an umbilical line or with a remote operated vehicle (ROV), while the inventive subject matter does not. Second, the inventive subject matter has particular advantages in relatively shallow holes offshore from a coastal jack-up or a geotechnical drilling ship because: 1) the inventive subject matter does not require a mobilization of a logging crew and winch, which are difficult and costly, and 2) the inventive subject matter does not require a time-based rig, which has significant cost. Third, the inventive subject matter is advantageous because the inventive subject matter has tools that record data in memory that is normally recorded by specialized logging engineers. Fourth, the inventive subject matter is advantageous in small diameter boreholes and boreholes having poor stability conditions because a full data log may be obtained with a relatively small and inexpensive tool in a relatively quick manner before the borehole destabilizes.

The above description is illustrative and explanatory of embodiments of the disclosed inventive subject matter. Various changes and modifications may be made to the embodiments within the scope of the disclosed inventive subject matter. The disclosed inventive subject matter therefore should be limited only by the following claims and their legal equivalents. 

1. A system comprising: a tool having an elongated body, a retarder positioned on the elongated body, and a locking ring positioned on the elongated body; and a bottom hole assembly, wherein the tool is engaged with the bottom hole assembly.
 2. The system of claim 1, wherein the bottom hole assembly comprises a drill bit having a central opening.
 3. The system of claim 2, wherein at least a portion of a lower section of the elongated body of the tool extends through the central opening of the drill bit when the tool is engaged with the bottom hole assembly.
 4. The system of claim 3, wherein the lower section of the elongated body comprises logging subs having sensors which are operational only in unlined boreholes.
 5. The system of claim 2, wherein the bottom hole assembly further comprises: a drill collar; a locking sub connected to the drill collar; and a saver sub connected to an end of the locking sub opposite the drill collar, wherein the drill bit is connected to an end of the saver sub opposite the locking sub.
 6. The system of claim 5, wherein the locking sub comprises a landing ring configured to engage the locking ring of the tool.
 7. The system of claim 1, wherein the tool is engaged with the bottom hole assembly after the tool free drops to the bottom hole assembly.
 8. The system of claim 1, wherein the retarder comprises at least one point of contact with an interior surface of a drill pipe.
 9. A method comprising: assembling a tool having a locking ring and a retarder positioned on an elongated body of the tool; providing a landing ring on a bottom hole assembly; free dropping the tool to the bottom hole assembly; and engaging the landing ring of the bottom hole assembly with the locking ring of the tool so that a portion of the tool extends below the bottom hole assembly.
 10. The method of claim 9, further comprising: logging data while pulling the engaged tool and bottom hole assembly upward through a borehole.
 11. The method of claim 10, wherein logging data while pulling comprises: stacking sonic signals during a stationary period.
 12. The method of claim 11, wherein stacking sonic signals comprises: adding together from about 10 to about 20 pulses from the tool during the stationary period.
 13. The method of claim 10, further comprising: recovering the logged data.
 14. The method of claim 9, further comprising: lifting a drill bit of the bottom hole assembly above the base of a borehole a distance approximately equal to a length of a portion of the tool below the locking ring of the tool minus a distance of the opposite end of the drill bit to the landing ring of the locking sub.
 15. The method of claim 9, further comprising: extending the portion of the tool below a drill bit of the bottom hole assembly in an unlined borehole, wherein the portion includes sensors that operate only in unlined boreholes.
 16. A tool comprising: an elongated body; a retarder positioned on the elongated body, wherein the retarder comprises at least one point of contact with an interior surface of a drill pipe; and a locking ring positioned on the elongated body.
 17. The tool of claim 16, wherein the elongated body comprises an upper section and a lower section, wherein the upper section comprises at least one logging sub which is operational in lined boreholes, wherein the lower section comprises at least one logging sub which is operational only in unlined boreholes
 18. The tool of claim 17, wherein the locking ring is positioned on the elongated body between the logging subs of the upper section of the elongated body and the logging subs of the lower section of the elongated body.
 19. The tool of claim 17, wherein the at least one logging sub of the lower section comprises a dipole sonic sensor.
 20. The tool of claim 16, wherein the retarder controls a speed of descent into a borehole. 